Butt welding apparatus, butt welding method, and butt welded product

ABSTRACT

A butt welding apparatus, a butt welding method, and a product manufactured by the butt welding method involves two electrode rollers disposed on both the front and back sides of a thick sheet member and a thin sheet member whose end surfaces are butted. The electrode rollers bridge across the sheet members and are composed of small diameter portions on the side of the thick sheet member and large diameter portions on the side of the thin sheet member. The small diameter portions come into contact with and press the thick sheet member before the large diameter portions come into contact with the thin sheet member. Thus, the end surface of the thick sheet member swells and deforms toward the thin sheet member and reliably comes into contact with the end surface of the thin sheet member, and power is applied between the end surfaces, even if not polished.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a butt welding apparatus for and a buttwelding method of melting and jointing a butt portion where end surfacesof two welding sheet members are butted to each other with electricresistance heat generated by power applied between a pair of twoelectrode members, and to a butt welded product manufactured by the buttwelding method.

2. Background Art

FIG. 21 shows a conventional butt welding apparatus. Two welding sheetmembers 101, 102 having the same thickness are set to the weldingapparatus with end surfaces 101A, 102A butted to each other. Each ofelectrode rollers 103, 104 disposed on both the front and back surfacesides of the sheet members 101, 102 has a thickness bridging across thesheet members 101, 102, and power is applied between the electroderollers 103, 104 when the sheet members 101, 102 are welded. When thepower is applied between the electrode rollers 103, 104 while they pressboth the sheet members 101, 102, the metal material of the sheet members101, 102 is melted and a nugget 105 is formed in the sheet members 101,102 at a central portion in the thickness thereof where an electricresistance is increased in the sheet members 101, 102 by the resistanceheat of the power flowing in the thickness direction of both the sheetmembers 101, 102. Further, since the power also flows through a pathpassing through a butt portion 106 where the end surfaces 101A, 102A arebutted to each other, the butt portion 106 is also melted at a centralportion in the thickness thereof by the heat generated by the contactresistance of these end surfaces 101A, 102A. Thus, the nugget 105 isformed so as to bridge across both the sheet members 101, 102.

Then, when the electrode rollers 103, 104 move along the butt portion106 while rolling or when the sheet members 101, 102 move with respectto the electrode rollers 103, 104 that are free to move at a definiteposition, the nugget 105, which can joint the sheet members 101, 102with a large amount of strength, is formed over the entire length of thebutt portion 106.

To form the nugget 105 bridging across both the sheet members 101, 102,an electrically conductive state must be secured by causing the endsurface 101A of the sheet member 101 to be butted to come into contactwith the end surface 102A of the sheet member 102. Thus, conventionally,both the end surfaces 101A, 102A are polished over the entire lengthsthereof prior to butt welding so as to secure a contact state of the endsurfaces 101A, 102A in the butt welding.

Therefore, conventionally, welding sheet members, for example, shearedin predetermined sizes by a shearing apparatus cannot be butt welded ina sheared state and must be subjected to finish processing to the endsurfaces 101A, 102A prior to a welding operation, which increases aworking cost and a working time.

An object of the present invention is to provide a butt weldingapparatus and a butt welding method capable of eliminating processingsuch as polishing, and the like for finishing the end surfaces of twowelding sheet members to be butted prior to butt welding, and to providea butt welded product capable of being manufactured by the butt weldingmethod.

DISCLOSURE OF THE INVENTION

In a butt welding apparatus according to the present invention having apair of two electrode members disposed on both the front and back sidesof two welding sheet members whose end surfaces are butted and eachhaving a thickness bridging across the welding sheet members for meltingthe butt portion of the two welding sheet members with electricresistance heat by supplying power between the electrode members andjointing the welding sheet members, the butt welding apparatus ischaracterized by comprising press portions formed in the pair ofelectrode members for pressing one of the two welding sheet members inthe thickness direction thereof and for swelling and deforming the endsurface of the one welding sheet member, which faces the other weldingsheet member, toward the other welding sheet member by pressing the onewelding sheet.

According to the butt welding apparatus, the pair of electrode membersare provided with the press portions by which the one of the two sheetmembers is pressed in the thickness direction of the sheet members, andthe end surface of the one sheet member, which faces the other sheetmember, is swelled and deformed toward the other sheet member by beingpressed, thereby the contact state of the end surfaces of the two sheetmembers is reliably secured.

Thus, it is not necessary to subject the end surfaces of the two sheetmembers to processing such as polishing and the like to finish themprior to butt welding, by which an overall job cost and an overallworking time can be reduced.

The butt welding apparatus according to the present invention can beapplied to cases in which two sheet members have various thicknesses andare butted in various butt states.

A first specific example of the cases resides in a case in which one ofthe two sheet members is a thick sheet member having a large thicknessand the other of them is a thin sheet member having a small thickness,and the thick sheet member is butted to the thin sheet member bydislocating the both the front and back surfaces of the thin sheetmember with respect to the both the front and back surfaces of the thicksheet member and by disposing the thin sheet member within the thicknessof the thick sheet member. In this case, each of the pair of electrodemembers has a first portion on the side of the thick sheet member and asecond portion on the side of the thin sheet member, the first andsecond portions being disposed side by side in the thickness directionof the electrode members, and the second portions project in the pressdirection with respect to the first portions acting as the pressportions.

According to the first specific example, when the thick sheet member ispressed by the first portions of the respective electrode members actingas the press portions, the end surface of the thick sheet member, whichfaces the thin sheet member, swells and deforms toward the thin sheetmember, and the end surface of the thick sheet member is caused toreliably come into contact with the end surface of the thin sheet memberby the swelling and deformation. Then, since the second portions of therespective electrode members come into contact with the thin sheetmember thereafter, the butt portion of the end surfaces of the two sheetmembers is melted by electric resistance heat by supplying power betweenthe electrode members until the second portions come into contact withthe thin sheet member. As a result, a nugget bridging across these sheetmembers is formed.

Note that, in the first example, the boundaries between the firstportions and the second portions of the respective electrode members maybe in agreement with the position of the butt portion of the thick andthin sheet members. However, it is preferable that the first portions ofthe respective electrode members have a thickness extending toward thethin sheet member across the butt portion.

According to the above arrangement, gaps are formed between the endsurface of the thick sheet member facing the thin sheet member and thesecond portions of the respective electrode members. Thus, when thethick sheet member is pressed by the first portions of the respectiveelectrode members, the end surface of the thick sheet member facing thethin sheet member can be reliably swelled and deformed toward the thinsheet member.

A second specific example resides in a case in which the two sheetmembers have the same thickness, and these sheet members are butted bycausing both the front and back surfaces of the sheet members to be inagreement with each other. In this case, each of the pair of electrodemembers has a first portion on the side of one of the two welding sheetmembers and a second portion on the side of the other of them, the firstand second portions being disposed side by side in the thicknessdirection of the electrode members, and the second portions retract in adirection opposite to the press direction with respect to the respectivefirst portions acting as the press portions.

According to the second specific arrangement, when the one of the twosheet members is pressed by the first portions of the respectiveelectrode members acting as the press portions, the end surface of theone sheet member facing the other sheet member swells and deforms towardthe other sheet member, and the end surfaces of the two sheet membersare caused to reliably come into contact with each other by the swellingand deformation. Then, since the second portions of the respectiveelectrode members come into contact with the other sheet memberthereafter, the butt portion of the end surfaces of the two sheetmembers is melted by electric resistance heat by supplying power betweenthe electrode members until the second portions come into contact withthe other sheet member. As a result, a nugget bridging across the sheetmembers is formed.

A third specific example resides in a case in which one of the two sheetmembers is a thick sheet member having a large thickness and the otherof them is a thin sheet member having a small thickness, and the thicksheet member is butted to the thin sheet member by causing one of boththe front and back surfaces of the thick sheet member to be in agreementwith one of both the front and back surfaces of the thin sheet memberwithout step. In this case, one of the pair of electrode membersdisposed on the side of the surfaces of the thick and thin sheet memberswhere a step is arisen has a first portion on the side of the thicksheet member and a second portion on the side of the thin sheet member,the first and second portions being disposed side by side in thethickness direction of the electrode members and the second portionprojecting more than the first portion in the press direction, the otherelectrode member comes into contact with both the thick and thin sheetmembers, and the portion of the other electrode member corresponding tothe thick sheet member and the first portion of the one electrode memberact as the press portions.

According to the third specific arrangement, when the thick sheet memberis pressed by the press portions of the respective electrode members,the end surface of the thick sheet member facing the thin sheet memberswells and deforms toward the thin sheet member, and the end surface ofthe thick sheet member is caused to reliably come into contact with theend surface of the thin sheet member by the swelling and deformation.Then, since the second portion of the one electrode member comes intocontact with the thin sheet member thereafter and both the electrodemembers are caused to come into contact with the thin sheet memberthereby, the butt portion of the end surfaces of the two sheet membersis melted by electric resistance heat by supplying power between theelectrode members until both the electrode members come into contactwith the thin sheet member. As a result, a nugget bridging across thesheet members is formed.

In the third example, the boundary between the first and second portionsof the one electrode member may be in agreement with the position of thebutt portion of the thick and thin sheet members. However, it ispreferable that the first portion of the electrode member have athickness extending toward the thin sheet member across the buttportion.

According to the above arrangement, a gap is formed between the endsurface of the thick sheet member facing the thin sheet member and thesecond portion of the one electrode member. Thus, when the thick sheetmember is pressed by the press portions of the pair of electrodemembers, the end surface of the thick sheet member facing the thin sheetmember can be reliably swelled and deformed toward the thin sheetmember.

Similarly to the third specific example, a fourth specific example alsoresides in a case in which one of the two sheet members is a thick sheetmember having a large thickness and the other of them is a thin sheetmember having a small thickness, the thick sheet member is butted to thethin sheet member by causing one of both the front and back surfaces ofthe thick sheet member to be in agreement with one of both the front andback surfaces of the thin sheet member without step. In the fourthspecific example, one of the pair of electrode members disposed on theside of the surfaces of the thick and thin sheet members in agreementwith each other without step has a first portion on the side of thethick sheet member and a second portion on the side of the thin sheetmember, the first and second portions being disposed side by side in thethickness direction of the electrode members, the first and secondportions project toward the thick and thin sheet members in the sameamount, the other of the electrode members also has a first portion onthe side of the thick sheet member and a second portion on the side ofthe thin sheet member, the first and second portions being disposed sideby side in the thickness direction of the electrode members, the secondportion of the first and second portions projects more than the firstportion toward the thin sheet member, the second portion of the oneelectrode member and the first portion of the other electrode memberhave electric conductivity, the first portion of the one electrodemember and the second portion of the other electrode member have anelectric insulating property, and the first portion of the one electrodemember and first portion of the other electrode member act as the pressportions.

According to the fourth specific example, when the thick sheet member ispressed by the first portions of the respective electrode members actingas the press portions, the end surface of the thick sheet member facingthe thin sheet member swells and deforms toward the thin sheet member,and the end surface of the thick sheet member is caused to reliably comeinto contact with the end surface of the thin sheet member by theswelling and deformation. Then, since the second portion of the oneelectrode member having the conductivity is in contact with the thinsheet member and the first portion of the other electrode member havingthe conductivity likewise is in contact with the thick sheet member,power flows through the path obliquely passing through the butt portionof the end surfaces of the thick and thin sheet members, thereby thebutt portion is melted by electric resistance heat, and, as a result, anugget bridging across the thick and thin sheet members is formed.

In the butt welded apparatus of the present invention including-therespective examples described above, the pair of two electrode membersmay be composed of electrode rollers that roll with respect to two sheetmembers or may be composed of block electrodes that have a lengthextending along the butt portion of two sheet members and act a pressload on the sheet members.

When the electrode members are composed of the latter block electrodes,a butt welding operation of two sheet members can be finished by a jobfor pressing the butt portion of these sheet members with the respectiveelectrode members once, which can reduce a butt welding working hoursand permits a multiplicity of butt welding operations to be carried outeffectively.

Further, when the electrode members are composed of the blockelectrodes, the butt portion of two sheet members may extend linearly ormay extend non-linearly. When the butt portion extends non-linearly, therespective electrode members are formed in a shape extending incorrespondence to the butt portion extending non-linearly.

That is, when the electrode members are composed of the blockelectrodes, two sheet members whose butt portion extends non-linearlycan be butt welded by the block electrodes, while it is impossible ordifficult to butt-weld them when the electrode members are composed ofelectrode rollers. The above arrangement is advantageous in that whentwo sheet members to be butted are manufactured from blank members byshearing them in arbitrary shapes according to, for example, the shapeand the like of a product manufactured from the two sheet members bybutting them, the two sheet members can be formed in any arbitrary buttshape.

Note that the term “non-linear shape” described above includes linearlines connected to each other while curving midway, a curved lineincluding a circular arc, a linear line connected to a curved line, andfurther a curved line connected to a curved line.

When the pair of two electrode members in the butt welding apparatus ofthe present invention are composed of the electrode rollers describedabove, the butt welding apparatus of the present invention may beprovided with a cooling liquid dropping unit for dropping a coolingliquid onto portions just behind the portions of two sheet members buttwelded by these electrode rollers.

According to the above arrangement, when a butt welding operation isexecuted using the pair of electrode rollers, the cooling liquiddropping unit drops the cooling liquid such as water, oil, and the likeonto the portions just behind the portions in the two sheet members buttwelded by the electrode rollers. It can be prevented or reduced bycooling the welded portions by dropping the cooling liquid onto themjust after they are welded that the two sheet members extend and deformand that the gap between the portions of the two sheet members to bewelded from now enlarges. Thus, one of the two sheet members is pressedby the press portions of the pair of electrode rollers and the endsurface of the one sheet member is swelled and deformed by pressing itas well as a more reliable contact state of the end surfaces of thesesheet members can be secured.

Further, the butt welding apparatus of the present invention may beprovided with an anti-oxidation gas supply unit for supplying ananti-oxidation gas such as an argon gas, a nitrogen gas, and the likeonto at least a portion butt welded by the pair of electrode members inthe two welding sheet members.

According to the above arrangement, a welding operation is executed inan anti-oxidization gas atmosphere, thereby the occurrence of rust at awelded butt portion can be prevented or reduced. As a result, when aproduct is made of a material of two butted sheet members, necessaryjobs such as a painting job and the like can be carried out asprescribed.

In a butt welding method according to the present invention of buttingend surfaces of two welding sheet members and jointing the butt portionof the two welding sheet members by melting the butt portion withelectric resistance heat by supplying power between a pair of twoelectrode members disposed on both the front and back sides of thewelding sheet members and each having a length bridging across thewelding sheet members, the butt welding method is characterized bycomprising the steps of pressing one of the two welding sheet members inthe thickness direction thereof by the pair of electrode members beingapplied with power and swelling and deforming the end surface of the onewelding sheet member, which faces the other welding sheet member, towardthe other welding sheet member, and securing the contact state betweenthe end surfaces through the swelling and deformation.

According to the butt welding method, one of the two sheet members ispressed by the pair of electrode members applied with the power in thethickness direction of the sheet members, and the end surface of the onesheet member facing the other sheet member is swelled and deformedtoward the other sheet member by pressing the one sheet member, therebythe contact state of the end surfaces of the two sheet members isreliably secured by the swelling and deformation.

The butt welding method can be also applied to cases in which two sheetmembers have various thicknesses and are butted in various butt statessimilarly to the butt welding apparatus described above.

A first specific example of the cases resides in a case in which one ofthe two sheet members is a thick sheet member having a large thicknessand the other of them is a thin sheet member having a small thickness,and the thick sheet member is butted to the thin sheet member bydislocating the both the front and back surfaces of the thin sheetmember with respect to the both the front and back surfaces of the thicksheet member and by disposing the thin sheet member within the thicknessof the thick sheet member. In this case, power is applied to the thicksheet member while pressing it by the pair of electrode members, and,thereafter, power is also applied to the thin sheet member by causingthe pair of electrode members to be in contact with the thin sheetmember. With this operation, the butt portion of the thick and thinsheet members is melted by electric resistance heat and a nuggetbridging across these sheet members is formed.

A second specific example resides in a case in which the two sheetmembers have the same thickness, and these sheet members are butted bycausing both the front and back surfaces of the sheet members to be inagreement with each other. In this case, power is applied to one of thetwo sheet members while pressing the one sheet member by the pair ofelectrode members, and, thereafter, power is also applied to the othersheet member by causing the pair of electrode members to come intocontact with the other sheet member. With this operation, the buttportion of the two sheet members is also melted by electric resistanceheat, thereby a nugget bridging across these sheet members is formed.

A third specific example resides in a case in which one of the two sheetmembers is a thick sheet member having a large thickness and the otherof them is a thin sheet member having a small thickness, and the thicksheet member is butted to the thin sheet member by causing one of boththe front and back surfaces of the thick sheet member to be in agreementwith one of both the front and back surfaces of the thin sheet memberwithout step. In this case, power is applied to the thick sheet memberwhile pressing it by the pair of electrode members, and, thereafter,power is also applied to the thin sheet member by causing the pair ofelectrode members to come into contact with the thin sheet member. As aresult, the butt portion of the thick and thin sheet members is meltedby electric resistance heat, thereby a nugget bridging across thesesheet members is formed.

A fourth specific example also resides in a case in which one of the twosheet members is a thick sheet member having a large thickness and theother of them is a thin sheet member having a small thickness, and thethick sheet member is butted to the thin sheet member by causing one ofboth the front and back surfaces of the thick sheet member to be inagreement with one of both the front and back surfaces of the thin sheetmember without step. In the fourth specific example, power is applied tothe thick and thin sheet members through a path obliquely passingthrough the butt portion by the pair of electrode members while pressingthe thick sheet member by these electrode members. With this operation,the butt portion of the thick and thin sheet members is also melted byelectric resistance heat, thereby a nugget bridging across these sheetmembers is formed.

A tailored blank manufactured by the butt welding apparatus and the buttwelding method according to the present invention described above can beused in any arbitrary applications by being subjected to post-processingsuch as press processing and the like executed thereafter, and oneexample of the applications is a vehicle body of a vehicle and anotherexample thereof is a main body of an electrical appliance.

Further, since a tailored blank manufactured by the third and fourthspecific examples described above of the butt welding method is formedin such a shape that one surface of a thick sheet member is jointed toone surface of a thin sheet member without step, the tailored blank canbe utilized as products having various applications making effectivelyuse of the feature of the shape.

As an example of the products, the tailored blank is used as an innerpanel coupled with an outer panel, a part of the vehicle body of thevehicle is formed of the outer panel and the inner panel, and thesurface on the side without step of the tailored blank is used as anoutward surface facing the outer panel.

According to this arrangement, since the surface on the side withoutstep is used as the outer surface facing the side of the outer panel,the part of the vehicle body of the vehicle can be formed using theouter panel, which has a good outside appearance that is not influencedby a step, on the outside of the vehicle body.

Further, when the part of the vehicle body of the vehicle is formed bycoupling the inner panel manufactured by the tailored blank with theouter panel, the part of the vehicle body may be arranged as a doorattached to the main portion of the vehicle body by hinges which can becoupled with the thick sheet member of the thick and thin sheet membersforming the inner panel.

According to the above arrangement, since the thick sheet member haslarge strength due to its large thickness, the hinges can be attached tothe thick sheet member making use of the strength thereof.

The door of the vehicle in this case may be a door attached to each sideof the vehicle or may be a back door that is also referred to as a tailgate.

An example of another application of the tailored blank manufactured bythe third and fourth specific examples described above of the buttwelding method resides in a dashboard panel of the vehicle formed of thetailored blank. The dashboard panel is composed of an upper side formedof the thin sheet member and a lower side formed of the thick sheetmember, and the surface without step faces a vehicle inside space suchas an engine room and the like disposed in front of a driver's seat.

According to the above arrangement, necessary strength can be secured bythe lower thick sheet member while reducing a vehicle weight by theupper thin sheet member. Further, the surface without step acts asurface on the side of the vehicle inside space which is exposed to theoutside of a compartment when a hood is opened, thereby the accumulationof rain water, which corrodes the butt portion of the thick and thinsheet members, can be prevented.

In the present invention, a positional relationship between the pair ofthe two electrode members and the two sheet members may be a positionalrelationship in which the two electrode members are disposed above andbelow the two sheet members both the front and back surfaces of whichface in an up and down direction or may be a positional relationship inwhich the two electrode members are disposed right and left of the twosheet members both the front and back surfaces of which face in a rightand left direction.

Further, the two sheet members in the present invention may be blanksbefore they are subjected to press processing for punching holes and thelike or may be sheet members having been subjected to the pressprocessing.

Further, in the present invention described above, the two sheet membersto be subjected to the butt welding means the number of sheet memberswhen they are butt welded to each other. Thus, the present inventionincludes a case in which a plurality of sheet members are disposed alongan end surface a single sheet member and they are subjected to the buttwelding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically showing a butt weldingapparatus according to an embodiment of the present invention;

FIG. 2 is a view showing a butted state of two sheet members shown inFIG. 1 at the cross-sectional position of the two sheet members whenbutt welding starts using electrode rollers as electrode members;

FIG. 3 is a view showing a state following the start of the butt weldingat the cross-sectional position of the same sheet members as those shownin FIG. 2;

FIG. 4 is a view showing a state further following the state of FIG. 3at the cross-sectional position of the same sheet members as those shownin FIG. 2;

FIG. 5 is a view showing a state in which the butt welding is finishedat the cross-sectional position of the same sheet members as those shownin FIG. 2;

FIG. 6 is a view showing butt welding according to another embodiment atthe cross-sectional position of two sheet members when welding starts;

FIG. 7 is a view showing a state in which the butt welding is finishedat the cross-sectional position of the same sheet members as those shownin FIG. 6 as to the embodiment of FIG. 6;

FIG. 8 is a view showing butt welding according to still anotherembodiment at the cross-sectional position of two sheet members whenwelding starts;

FIG. 9 is a view showing a state in which the butt welding is finishedat the cross-sectional position of the same sheet members as those shownin FIG. 8 as to the embodiment of FIG. 8;

FIG. 10 is a view showing butt welding according to a further embodimentat the cross-sectional position of two sheet members when weldingstarts;

FIG. 11 is a view showing a state in which the butt welding is finishedat the cross-sectional position of the same sheet members as those shownin FIG. 10 as to the embodiment of FIG. 10;

FIG. 12 is a side elevational view of a vehicle using a productmanufactured from a tailored blank composed of thick and thin sheetmembers according to the embodiment of FIGS. 8 and 9 and the embodimentof FIGS. 10 and 11 as an inner panel of a door disposed to a side of thevehicle;

FIG. 13 is a sectional perspective view of a main portion of the door ofFIG. 12;

FIG. 14 is a sectional view of FIG. 13 taken along a line S14-S14;

FIG. 15 is a back perspective view of a vehicle using a productmanufactured from a tailored blank composed of thick and thin sheetmembers according to the embodiment of FIGS. 8 and 9 and the embodimentFIGS. 10 and 11 as an inner panel of a back door;

FIG. 16 is a perspective view of a dashboard lower panel as a productmanufactured from a tailored blank composed of thick and thin sheetmembers according to the embodiment of FIGS. 8 and 9 and the embodimentFIGS. 10 and 11 when the dashboard lower panel is viewed from the sideof a vehicle inside space such as an engine room and the like disposedin front of a driver's seat;

FIG. 17 is a longitudinal sectional view of the dashboard lower panel ofFIG. 16;

FIG. 18 is a perspective view schematically showing a butt weldingapparatus that shows an embodiment using block electrodes as electrodemembers;

FIG. 19 is a plan view of FIG. 18;

FIG. 20 is a view similar to FIG. 19 and shows an embodiment in whichthe block electrodes as the electrode members extend non-linearly incorrespondence to the butt portion of two sheet members; and

FIG. 21 is a view showing a conventional butt welding apparatus at thecross-sectional position of sheet members.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described below in more detail withreference to the accompanying drawings. FIG. 1 is a perspective viewschematically showing a butt welding apparatus according to anembodiment. Two welding sheet members 1, 2 each composed of a steelsheet or another metal sheet are butted and fixedly set to a work table10 by fixtures 11, 12. One of the sheet members is a thick sheet member1 having a large thickness and the other of them is a thin sheet member2 having a small thickness.

The butt portion 6 of an end surface 1A of the thick sheet member 1 andan end surface 2A of the thin sheet member 2 shown in FIG. 2 is inagreement with the position of a slender opening 10A of the work table10 shown in FIG. 1, and a pair of two electrode rollers 3, 4 acting aselectrode members are disposed above and below the slender opening 10A,in other words, on both the front and back sides of the two sheetmembers 1, 2 to butt weld the butt portion 6 with electric resistanceheat. The upper electrode roller 3 of the electrode rollers 3, 4 eachhaving a thickness bridging across the sheet members 1, 2 moves up anddown with respect to the work table 10, the lower electrodes roller 4also moves up and down at a position where it is inserted into theopening 10A, and these electrode rollers 3, 4 abut against the sheetmembers 1, 2 and execute butt welding. Further, in the welding, the worktable 10 moves in the lengthwise direction of the butt portion 6,thereby the butt portion 6 is melted over its entire length by theelectric resistance heat in the sheet members 1, 2 and jointed by theelectrode rollers 3, 4 that roll while being applied with power in thewelding.

The welding apparatus according to the embodiment is provided with acooling liquid dropping unit 13 for dropping a cooling liquid such aswater or oil onto the portions just behind the portions of the two sheetmembers 1, 2 butt welded by the electrode rollers 3, 4. Further, thewelding apparatus is also provided with an anti-oxidation gas supplyunit 14 for supplying an anti-oxidation gas such as an argon gas, anitrogen gas, etc. onto the portions of the sheet members 1, 2 to bewelded by the electrode rollers 3, 4.

As shown in FIG. 2, the thick sheet member 1 is butted to the thin sheetmember 2 by dislocating both the front and back surfaces of the thinsheet member 2 from those of the thick sheet member 1 and by disposingthe thin sheet member 2 within the thickness of the thick sheet member1. This butt state is realized by providing a step member such as aspacer and the like, which forms a step between both the sheet members1, 2, with the work table 10 and/or each of the fixtures 11 and 12 shownin FIG. 1.

Further, as shown in FIG. 2, the two electrode rollers 3, 4 are composedof first portions 3A, 4A disposed on the side of the thick sheet member1 and second portions 3B, 4B disposed on the side of the thin sheetmember 2, the first and second portions 3A, 4A and 3B, 4B being disposedside by side in the thickness direction of these electrode rollers 3, 4,and the second portions 3B, 4B project more than the first portions 3A,4A in an inward direction of the thickness of sheet members 1, 2, inother words, in a direction where the electrode rollers 3, 4 press thesheet members 1, 2.

That is, since the electrode members according to the embodiment arecomposed of the electrode rollers 3, 4 in rotation, the first portions3A, 4A constitute the small diameter portions of the electrode rollers3, 4 as well as the second portions 3B, 4B constitute the large diameterportions of the electrode rollers 3, 4. An amount of projection of thesecond portions 3B, 4B with respect to the first portions 3A, 4A is setto such an amount that when the first portions 3A, 4A abut against thethick sheet member 1, the second portions 3B, 4B do not come intocontact with the thin sheet member 2.

Further, step portions 3C, 4C acting as boundaries between the firstportions 3A, 4A and the second portions 3B, 4B are not in agreement withthe position of the butt portion 6 and are dislocated toward the thinsheet member 2. Thus, the first portions 3A, 4A have a thicknessextending toward the thin sheet member 2 across the butt portion 6.Accordingly, when the first portions 3A, 4A abut against the thick sheetmember 1, gaps 7, 8 are formed between the end surface 1A of the thicksheet member 1 facing the thin sheet member 2 and the second portions3B, 4B.

FIG. 2 shows a state in which the butt welding is started by theelectrode rollers 3, 4, FIGS. 3 to 5 show subsequent processes of thebutt welding at the cross-sectional position of the same sheet members1, 2 as those shown in FIG. 2 according to the sequence of theprocesses.

As shown in FIG. 2, the butt welding is started by pressing the thicksheet member 1 with the first portions 3A, 4A of the electrode rollers3, 4. Thus, the first portions 3A, 4A act as press portions for pressingthe thick sheet member 1. Further, at the time, power starts to beapplied between the electrode rollers 3, 4.

As shown in FIG. 3, when the thick sheet member 1 is more pressed by thefirst portions 3A, 4A, the end surface 1A of the thick sheet member 1starts to be swelled and deformed toward the thin sheet member 2 in thegaps 7 and 8 by pressing thick sheet blank 1, and the end surface 2A ofthe thin sheet member 2 coming into contact with the end surface 1A ofthe thick sheet member 1 due to the swelling and deformation starts toflatly deform in an outward direction of the thickness of the thin sheetmember 2.

As described above, when the end portion 1B of the thick sheet member 1on the side of the end surface 1A thereof is pressed in the thicknessdirection of the thick sheet member 1 by the first portions 3A, 4A ofthe electrode rollers 3, 4, the end surface 1A deforms so as to swelltoward the thin sheet member 2. Thus, even if the end surfaces 1A, 2A ofthe thick and thin sheet members 1, 2 prior to the butt welding remainin a state, in which they are sheared from blank members to manufacturethe thick and thin sheet members 1 and 2, and are not subjected tofinish processing such as polishing and the like, the end surface 1Areliably comes into contact with the end surface 2A in the butt welding.

When the thick sheet member 1 is much more pressed by the first portions3A, 4A from the state shown in FIG. 3, a nugget 5 starts to be formed inthe thick sheet member 1 applied with power from the electrode rollers3, 4 at a central portion in the thickness thereof where an electricresistance value is maximized as well as the end surface 1A of the thicksheet member 1 further swells and deforms toward the thin sheet member2, and the end surface 2A of the thin sheet member 2 more flatly deformsin the outward direction of the thickness thereof, as shown in FIG. 4.

Then, when the butt welding is finished, the thick sheet member 1 isfurther much more pressed by the first portions 3A, 4A as shown in FIG.5. Thus, the second portions 3B, 4B of the electrode rollers 3, 4 comeinto contact with and presses the end surface 2B of the thin sheetmember 2, the end surface 2B being a portion near to the end surface 2Aof the thin sheet member 2 and swelling in the outward direction of thethickness of the sheet so that the wall thickness thereof is increased.

Thus, at the time, the power from the electrode rollers 3, 4 is alsoapplied to the thin sheet member 2, thereby the nugget 5 is also formedat a central portion of the thin sheet member 2 in the thickness thereofas well as the power is also applied through a path passing through thebutt portion 6 of the end surfaces 1A, 2A in contact with each other.Therefore, a material in the vicinity of the butt portion 6 is alsomelted with the heat generated by the contact resistance of the endsurfaces 1A, 2A, and, as a result, the nugget 5 bridges across the thickand thin sheet members 1, 2.

While the above-mentioned is an explanation as to the samecross-sectional positions of the two sheet members 1, 2 to be buttwelded, the butt welding, which proceeds from the state shown in FIG. 2to the state shown in FIG. 5 using the pair of two electrode rollers 3,4, is executed over the entire length of the butt portion 6 by movingthe work table 10 shown in FIG. 1 and rolling the electrode rollers 3, 4with respect to the sheet members 1, 2 by the move.

Further, when the butt welding is executed as described above, thecooling liquid is dropped from the cooling liquid dropping unit 13 shownin FIG. 1 onto the portions just behind the portions in the two sheetmembers 1, 2 welded by the electrode rollers 3, 4, and the sheet members1, 2 are butt welded over the entire lengths thereof while the coolingliquid is being dropped. The cooling executed by dropping the coolingliquid can prevent the expansion and deformation of the two sheetmembers 1, 2 by which the gap between the portions to be welded from nowof the two sheet members 1, 2 is enlarged.

Further, the anti-oxidization gas is supplied from the anti-oxidationgas supply unit 14 onto the portions of the sheet members 1, 2 to bewelded by the electrode rollers 3, 4. Thus, the butt welding of thesheet members 1, 2 is executed while preventing the occurrence of rustat the butt portion 6 having been welded.

According to the embodiment described above, the electrode rollers 3, 4are provided with the first portions 3A, 4A to press the thick sheetmember 1 at the start of the butt welding and to swell and deform theend surface 1A of the thick sheet member 1 toward the thin sheet member2 by pressing it, which permits the end surface 1A to reliably come intocontact with the end surface 2A of the thin sheet member 2. Thus, it isnot necessary to execute processing for finishing the end surfaces 1A,2A by polishing and the like as pre-processing to be executed prior tothe butt welding, and the butt welding can be executed to the endsurfaces 1A, 2A which remain in the state when they were sheared by theshearing apparatus, thereby a working cost of an entire weldingoperation including the pre-processing can be reduced, a working timecan be decreased, and workability can be improved.

Then, since the electrode rollers 3, 4 are provided with the secondportions 3B, 4B that come into contact with the thin sheet member 2, apower application path passing through the butt portion 6 is formed bythe contact of the second portions 3B, 4B with the thin sheet member 2and the contact of the first portions 3A, 4A with the thick sheet member1. Thus, the nugget 5 formed at the central portions of the thick andthin sheet members 1, 2 in the thickness directions thereof bridgesacross thick and thin sheet members 1, 2 by melting a central portion ofthe butt portion 6 in the thickness thereof by the electric resistanceheat, which can increase the joint strength of the welded thick and thinsheet members 1, 2.

Further, the first portions 3A, 4A of the electrode rollers 3, 4 actingas the press portions for pressing the thick sheet member 1 reach thethin sheet member 2 across the butt portion 6. Thus, when the firstportions 3A, 4A press the thick sheet member 1, the end surface 1A ofthe thick sheet member 1 can be swelled and deformed in the gaps 7 and 8formed between the end surface 1A and the second portions 3B, 4B,thereby the end surface 1A can be caused to reliably come into contactwith the end surface 2A of the thin sheet member 2.

Further, according to the embodiment, while the portions of the twosheet members 1, 2 just after welded by the electrode rollers 3, 4 aremade to a high temperature by the heat of the welding, they are cooledwith the cooling liquid dropped from the cooling liquid dropping unit13. Thus, the expansion and deformation, which is arisen when theportions just after being welded remain at the high temperature andincreases the gap between portions to be welded from now, can beeliminated or reduced. Accordingly, the end surface 1A of the thicksheet member 1 can be swelled and deformed toward the thin sheet member2 by the first portions 3A, 4A of the electrode rollers 3, 4 as well asthe end surfaces 1A, 2A can be caused to more reliably come into contactwith each other.

Further, according to the embodiment, since the anti-oxidization gas issupplied from the anti-oxidation gas supply unit 14 to the portions ofthe two sheet members 1, 2 to be butt welded by the electrode rollers 3,4, the butt welding is executed in an anti-oxidization gas atmosphere,which can eliminate or reduce the occurrence of rust at the butt portion6 having been welded. As a result, when a product is manufactured from amaterial of a tailored blank composed of the two butted sheet members 1,2, necessary jobs such as a painting job and the like can be carried outas prescribed.

FIGS. 6 and 7 show another embodiment. Two welding sheet members 21, 22in the embodiment have the same thickness, and these sheet members 21,22 are butted with both the front and back surfaces thereof in agreementwith each other. A pair of two electrode rollers 23, 24 disposed on boththe front and back sides of the sheet members 21, 22 are composed offirst portions 23A, 24A disposed on the side of one of the sheet members21 and 22, that is, the sheet member 21 and second portions 23B, 24Bdisposed on the side of the other sheet member 22 also in thisembodiment, the first and second portions 23A, 24A and 23B, 24B beingdisposed side by side in the thickness direction of these electroderollers 23, 24.

Then, in this embodiment, the second portions 23B, 24B retract in adirection opposite to the press direction of the first portions 23A, 24Aacting as press portions for pressing the sheet member 21 in thethickness direction thereof. That is, in the embodiment, the firstportions 23A, 24A constitute the large diameter portions of theelectrode rollers 23, 24, and the second portions 23B, 24B constitutethe small diameter portions thereof.

FIG. 6 shows a state in which butt welding is started by the electroderollers 23, 24, and FIG. 7 shows a state in which the butt welding isfinished at the cross-sectional position of the same sheet members 21,22 as those shown in FIG. 6. The butt welding starts when the firstportions 23A, 24A press an end portion 21B of the sheet member 21 nearto an end surface 21A thereof, thereby the end surface 21A swells anddeforms toward the sheet member 22 as the end portion 21B is pressed.Thus, the end surfaces 21A, 22A of both the sheet members 21, 22reliably come into contact with each other.

When the sheet member 21 is pressed by the first portions 23A, 24A to astate shown in FIG. 7, an end portion 22B of the sheet member 22 near tothe end surface 22A thereof is swelled and deformed in an outwarddirection of the thickness of the sheet member and its wall thickness isincreased by the swelled and deformed end surface 21A of the sheetmember 21. Thus, the second portions 23B, 24B come into contact with theend portion 22B and press the sheet member 22. Accordingly, at the time,a nugget 25 is formed at a central portion in the thickness of the sheetmember 21 by the power applied from the first portions 23A, 24A as wellas the nugget 25 is also formed at a central portion of the sheet member22 in the thickness by the power applied from the second portions 23B,24B. Further, since a power application path is formed in a butt portion26 where the end surfaces 21A, 22A are butted to each other, the nugget25 bridges across the two sheet members 21, 22.

Thus, even if the end surfaces 21A, 22A of the two sheet members 21, 22are not finished by polishing and the like prior to the butt welding ofthem, a reliable contact state of the end surfaces 21A, 22A can besecured by the action of the first portions 23A, 24A of the electroderollers 23, 24 as the press portions also in the embodiment. As aresult, the power application path passing through the butt portion 26is formed, and the nugget 25 bridging across the sheet members 21, 22can be formed.

Note that, in the embodiment, the boundaries between the first portions23A, 24A and the second portions 23B, 24B are in agreement with theposition of the butt portion 26 of the two sheet members 21 and 22 asshown in FIGS. 6 and 7. However, an effect similar to that describedabove can be obtained even if the boundaries are somewhat dislocatedfrom the butt portion 26 toward the sheet member 21.

FIGS. 8 and 9 show still another embodiment. One of two sheet members31, 32 in the embodiment is a thick sheet member 31 having a largethickness, and the other of them is a thin sheet member 32 having asmall thickness. The thick sheet member 31 is butted to the thin sheetmember 32 with the back surface of the thick sheet member 31 inagreement with the back surface of the thin sheet member 32 withoutstep.

Further, of a pair of two electrode rollers 33, 34 disposed on both thefront and back sides of these sheet members 31, 32, the electrode roller33 disposed on the front surface side of the thick and thin sheetmembers 31, 32 has a first portion 33A on the side of the thick sheetmember 31 and a second portion 33B on the side of the thin sheet member32, the first and second portions 33A and 33B being disposed side byside in the thickness direction of the electrode roller 33, and thesecond portion 33B projects more than the first portion 33A in a pressdirection that is an inward direction of the thickness of the sheetmember. Further, the electrode roller 34 disposed on the back surfacesides of the thick and thin sheet members 31, 32 has a thicknessbridging across them similarly to the electrode roller 33. However, theelectrode roller 34 is not formed in a shape having portions divided toeach of the thick and thin sheet members 31, 32.

Thus, in this embodiment, only the electrode roller 33 is arranged as aroller with a step composed of large and small diameter portionssimilarly to the electrode rollers 3, 4, 23, 24 in the embodimentsdescribed above. However, the electrode roller 34 is arranged as aroller without step having the same diameter continuous in the thicknessdirection thereof. The electrode roller 34 comes into contact with thetwo sheet members 31, 32 at the same time.

Further, a step portion 33C acting as the boundary between the first andsecond portions 33A, 33B of the electrode roller 33 is not in agreementwith the position the butt portion 36 of the sheet members 31, 32 and isdislocated toward the thin sheet member 32. Thus, the first portion 33Ahas a thickness extending toward the thin sheet member 32 across thebutt portion 36. Thus, when the first portion 33A abuts against thethick sheet member 31, a gap 37 is formed between an end surface 31A ofthe thick sheet member 31 facing the thin sheet member 32 and the secondportion 33B.

FIG. 8 shows a state in which butt welding is started by the electroderollers 33, 34, and FIG. 9 shows a state in which the butt welding isfinished at the cross-sectional position of the same sheet members 31,32 as those shown in FIG. 8. The butt welding starts when the firstportion 33A of the electrode roller 33 and the portion of the electroderoller 34 corresponding to the thick sheet member 31 act as pressportions and press an end portion 31B of the thick sheet member 31 nearto the end surface 31A thereof. As the end portion 31B is pressed, theend surface 31A swells and deforms toward the thin sheet member 32.Thus, the end surfaces 31A, 32A of both the sheet members 31, 32reliably come into contact with each other.

When the thick sheet member 31 is pressed to a state shown in FIG. 9, anend portion 32B of the thin sheet member 32 near to the end surface 32Athereof is swelled and deformed in an outward direction of the thicknessof the sheet member by the press load from the swelled and deformed endsurface 31A of the thick sheet member 31. Accordingly, at the time, thesecond portion 33B of the electrode roller 33 comes into contact withthe end portion 32B which presses the thin sheet member 32 together withthe portion of the electrode roller 34 corresponding to the thin sheetmember 32.

Therefore, at the time of FIG. 9, power is applied to both the thick andthin sheet members 31, 32 by the electrode rollers 33, 34. Thus, by thetime at the latest, a nugget 35 is formed at a central portion of thethick sheet member 31 in the thickness direction thereof by the powerapplied thereto as well as the nugget 35 is also formed at a centralportion of the thin sheet member 32 in the thickness thereof, andfurther a power application path is formed in the butt portion 36 of theend surfaces 31A, 32A, thereby the nugget 35 bridges across the twosheet members 31, 32.

Thus, the end surfaces 31A, 32A of the two sheet members 31, 32 can becaused to reliably come into contact with each other even if they arenot subjected to finish processing such as polishing and the like priorto the butt welding of them also in this embodiment. As a result, thenugget 35 bridging across the sheet members 31, 32 can be formed.

Further, in this embodiment, since the first portion 33A of theelectrode roller 33 has a thickness extending toward the thin sheetmember 32 across the butt portion 36 of the thick and thin sheet members31, 32, the gap 37 is formed between the end surface 31A of the thicksheet member 31 facing the thin sheet member 32 and the second portion33B of the electrode roller 33. Therefore, when the thick sheet member31 is pressed by the electrode rollers 33, 34, the end surface 31A ofthe thick sheet member 31 can be reliably swelled and deformed towardthe thin sheet member 32 in the gap 37.

FIGS. 10 and 11 show a further embodiment. One of two sheet members is athick sheet member 31 having a large thickness, and the other of them isa thin sheet member 32 having a small thickness also in this embodiment.The thick sheet member 31 is butted to the thin sheet member 32 with thefront surface of the thick sheet member 31 in agreement with that of thethin sheet member 32 without step.

Further, of a pair of two electrode rollers 43, 44 disposed on both thefront and back sides of the sheet members 31, 32, the electrode roller43 disposed on the front surface side of the thick and thin sheetmembers 31, 32 has a first portion 43A on the side of the thick sheetmember 31 and a second portion 43B on the side of the thin sheet member32, the first and second portions 43A and 43B being disposed side byside in the thickness direction of the electrode roller 43. The firstand second portions 43A and 43B project toward the thick and thin sheetmembers 31, 32 in the same amount. The electrode roller 44 disposed onthe back surface sides of the thick and thin sheet members 31, 32 alsohave a first portion 44A on the side of the thick sheet member 31 and asecond portion 44B on the side of the thin sheet member 32, the firstand second portions 44A and 44B being disposed side by side in thethickness direction of the electrode roller 44. The second portion 44Bof these first and second portions 44A, 44B projects more than the firstportion 44A toward the thin sheet member 32.

Thus, in this embodiment, only the electrode roller 44 is arranged as aroller with a step composed of a large diameter portion and a smalldiameter portion.

Further, in this embodiment, the second portion 43B of the electroderoller 43 and the first portion 44A of the electrode roller 44 haveelectric conductivity because they are formed of an electricallyconductive metal such as copper and the like. In contrast, the firstportion 43A of the electrode roller 43 and the second portion 44B of theelectrode roller 44 have an electric insulating property because theyare formed of an electrically insulating material such as ceramics andthe like. That is, in the embodiment, at least the outer peripheralportions of the electrode rollers 43, 44 in contact with the sheetmembers 31, 32 are formed of different kinds of materials superimposedin the thickness directions thereof.

In this embodiment, when butt welding starts, an end portion 31B of thethick sheet member 31 near to an end surface 31A thereof is pressed bythe first and second portions 43A, 44A of the electrode rollers 43, 44.Thus, these first and second portions 43A, 44A act as press portions.

Further, in this embodiment, the boundaries between the first portions43A, 44A and the second portions 43B, 44B are in agreement with theposition of the butt portion 36 of the thick and thin sheet members 31,32, and recessed portions 43C, 44C, which recess in an inside diameterdirections of the electrode rollers 43, 44 are formed in theseboundaries. Spaces 47, 48 are formed by the recessed portions 43C, 44Cand permit the end surface 31A of the thick sheet member 31 facing thethin sheet member 32 to swell and deform toward the thin sheet member 32even outside of the thickness of the thin sheet member 32.

FIG. 10 shows a state in which the butt welding is started by theelectrode rollers 43, 44, and FIG. 11 shows a state in which the buttwelding is finished at the cross-sectional position of the same sheetmembers 31, 32 as those shown in FIG. 10. The butt welding starts whenthe first portions 43A, 44A press the end portion 31B of the thick sheetmember 31 near to the end surface 31A thereof, thereby the end surface31A swells and deforms toward the thin sheet member 32 as the endportion 31B is pressed. Thus, the end surface 31A of the thick sheetmember 31 reliably comes into contact with the end surface 32A of thethin sheet member 32.

When the thick sheet member 31 is pressed by the first portions 43A, 44Ato a state shown in FIG. 11, the second portion 44B of the electroderoller 44 comes into contact with the thin sheet member 32 and pressesthe thin sheet member 32 together with the second portion 43B of theelectrode roller 43 having come into contact with the thin sheet member32.

Thus, by this time at the latest, a power application path obliquelypassing through the butt portion 36 of the end surface 31A of the thicksheet member 31 and the end surface 32A of the thin sheet member 32 ismade by the second portion 43B of the electrode roller 43 and the firstportion 44A of the electrode roller 44 each having the electricconductivity. Therefore, power is also applied to the thick and thinsheet members 31, 32, thereby the nugget 35 bridging across these sheetmembers 31, 32 is formed.

Accordingly, even if the end surfaces 31A, 32A of the two sheet members31, 32 are not subjected to finish processing such as polishing and thelike prior to the butt welding thereof, a reliable contact state of theend surfaces 31A, 32A can be secured also in this embodiment. As aresult, the nugget 35 bridging across the sheet members 31, 32 can beformed by the power application path passing through the butt portion36.

Further, in this embodiment, the recessed portions 43C, 44C are formedin the boundaries between the first portions 43A, 44A of the electroderollers 43, 44 and the second portions 43B, 44B thereof, thereby thespaces 47, 48 are formed from the end surface 31A toward the thin sheetmember 32 and permit the end surface 31A of the thick sheet member 31 toswell and deform toward the thin sheet member 32 also outside of thethickness of the thin sheet member 32. As a result, when the thick sheetmember 31 is pressed by the first portions 43A, 44A, the end surface 31Aof the thick sheet member 31 can be reliably swelled and deformed towardthe thin sheet member 32 side, and contact state of the end surface 31Aof the thick sheet member 31 with the end surface 32A of the thin sheetmember 32 can be secured.

In addition, in the embodiment of FIGS. 10 and 11, the front and backsurfaces of the two sheet members 31, 32 may be reversed and the backsurface of the thick sheet member 31 may be in agreement with the backsurface of the thin sheet member 32 without step similarly to theembodiment of FIGS. 8 and 9, the up/down relationship of the twoelectrode rollers 43, 44 may be reversed.

According to the respective embodiments described above, tailored blankscomposed of the two sheets 1 and 2, 21 and 22, and 31 and 32 can bemanufactured. These tailored blanks are subjected to prescribedprocessing such as press processing and the like so that they can bemade to products used in various applications.

FIG. 12 shows a vehicle body 50 of a four-wheel vehicle using a productmanufactured by subjecting the tailored blank made of the thick and thinsheet members 31, 32 according to the embodiment of FIGS. 8 and 9 andthe embodiment of FIGS. 10 and 11 to press processing. The vehicle body50 has a vehicle main body 51 and doors 52 attached to the side surfacesof the vehicle main body 51 so as to open and close through hinges 53.As shown in FIG. 13, each of the doors 52 is formed by coupling an outerpanel 54 outside of the vehicle with an inner panel 55 inside of thevehicle, and they are coupled by hemming processing for pressing theturned-back peripheral edge 54A of the outer panel 54 against theperipheral edge 55A of the inner panel 55.

The inner panel 55 is manufactured by subjecting the tailored blankcomposed of the thick and thin sheet members 31, 32 manufactured by thebutt welding of the embodiment of FIGS. 8 and 9 and the embodiment ofFIGS. 10 and 11 to press processing. The inner panel 55, which is aproduct manufactured from the tailored blank, is coupled with the outerpanel 54 in which a surface 55B without step of the thick and thin sheetmembers 31, 32 acts as an outward surface facing the outer panel 54, asshown in FIG. 14 that is a sectional view taken along the line S14-S14of FIG. 13.

Further, the hinges 53 of FIG. 12 are coupled with the portion of thethick sheet member 31 of the portions forming the inner panel 55 of thethick and thin sheet member 31 and 32.

According to this embodiment, the inner panel 55 is composed of thetailored blank made of the thick and thin sheet members 31 and 32 whichare butt welded such that one surfaces thereof have no step, and thesurface 55B without step of the inner panel 55 is arranged as theoutward surface facing the outer panel 54. Therefore, when door 52 ismanufactured by coupling the inner panel 55 with the outer panel 54 bythe hemming processing, the outside surface of the door 52 can beprovided with a good outside appearance that is not influenced by astep.

Further, since the hinges 53 are coupled with the portion of the thicksheet member 31 having a large thickness and a large strength, they canbe attached to the door 52 making use of the strength of the thick sheetmember 31. Moreover, the overall weight of the door 52 can be reduced bythe thin sheet member 32.

The product manufactured by forming the tailored blank in thepredetermined shape by the press processing is used as the inner panelof the door of the vehicle as described above, which can be also appliedto a back door 62 that is attached to a four-wheel vehicle main body 61through hinges 63 and formed by coupling an outer panel with an innerpanel as shown in FIG. 15 similarly to the above door 52.

FIGS. 16 and 17 show another application of the tailored blank. FIG. 16is a perspective view of a dash board lower panel 71 of an FF (frontengine, front drive) and FR (front engine, rear drive) four-wheelvehicle when it is viewed from the side of a vehicle inside space 72such an engine room and the like disposed in front of a driver's seat.The dash board lower panel 71, which has two side frames 73 whose baseend portions are coupled in order to reinforce a vehicle body, is formedby subjecting the tailored blank composed of the thick and thin sheetmembers 31, 32 to press processing. Further, as shown in FIG. 17 that isa longitudinal sectional view of the dash board lower panel 71, the dashboard lower panel 71 is formed of the thin sheet member 32 acting as anupper side and the thick sheet member acting as a lower side 31 as wellas a surface 71A without step faces the side of the vehicle inside space72.

According to the above arrangement, necessary strength can be secured bythe lower thick sheet member 31 while reducing a vehicle weight by theupper thin sheet member 32. Further, the surface 71A without step actsas a surface on the side of the vehicle inside space 72 which is exposedoutside of a compartment when a hood is opened, thereby the accumulationof rain water, which corrodes the butt portion 36 of the thick and thinsheet members, can be prevented.

While the pair of two electrode members in the butt welding apparatus inthe respective embodiments described in FIGS. 1 to 11 are composed ofthe electrode rollers, electrode members in an embodiment of FIGS. 18and 19 are composed of block electrodes 83 and 84 mounted on a pressapparatus.

That is, in the embodiment of FIGS. 18 and 19, the block electrode 83 isdisposed on an upper side that is the front surfaces side of the thickand thin sheet members 1, 2 as welding sheets, and the block electrode84 is disposed on a lower side that is the back surfaces side of thethick and thin sheet members 1, 2. Each of the block electrodes 83, 84has a thickness bridging across the thick sheet member 1 and across thethin sheet member 2. Further, each of the block electrodes 83, 84 has alength linearly extending along the butt portion 6 of the sheet members1, 2 as shown in FIG. 19 that is a plan view of FIG. 18. The blockelectrode 83 is attached to a rising/falling member such as a slide andthe like moving up and down of the press apparatus, and the blockelectrode 84 is attached onto an upper surface of a table member 88coupled with an unmovable member such as a bolster and the like of thepress apparatus. The table member 88 has fixtures 11, 12 for butting thethick sheet member 1 to the thin sheet member 2 in a predeterminedpositional relationship and fixedly setting them on the table member 88.

When the upper block electrode 83 falls with respect to the table member88, the block electrodes 83, 84 press the butt portion 6, and the pressload of them is acts on the thick and thin sheet members 1, 2. At thistime, power is applied between the block electrodes 83, 84.

Since the sheet members 1, 2 shown in FIG. 18 are the same as those inthe embodiment of FIGS. 1 to 5, the block electrodes 83 and 84 have thesame cross sectional shapes as the outer peripheral portions of theelectrode rollers 3, 4 shown in FIGS. 1 to 5. Thus, butt welding of thethick and thin sheet members 1, 2 executed by moving the block electrode83 downward is proceeded in the same sequence as that of FIGS. 2, 3, 4,and 5 also in this embodiment, and the same operation/working effect asthat of the embodiment of FIGS. 1 to 5 can be obtained.

In particular, according to this embodiment, since the electrode membersare composed of the block electrodes 83, 84, a butt welding operationfor one set of the two sheet members 1, 2 can be finished by pressingthe butt portion 6 of them by the block electrodes 83, 84 only once.Thus, a time of the butt welding operation can be reduced and efficiencyof a multiplicity of butt welding operations can be improved.

Note that, in this embodiment, when the two sheet members are the sameas those of the embodiment of FIGS. 6 and 7, the sectional shapes of theblock electrodes 83, 84 are formed similarly to the outer peripheralportions of the electrode rollers of the embodiment of FIGS. 6 and 7.Further, when the two sheet members are the same as those of theembodiment of FIGS. 8 and 9 and those of the embodiment of FIGS. 10 and11, the sectional shapes of the block electrodes 83 and 84 are formedsimilarly to the outer peripheral portions of the electrode rollers ofthe embodiment of FIGS. 8 and 9 and the embodiment of FIGS. 10 and 11.

FIG. 20 shows another embodiment when the pair of two electrode membersare composed of block electrodes. Since end surfaces of two sheetmembers 91 and 92 in this embodiment are composed of linear linesjointed to each other at right angles, a butt portion 96 formed bybutting these end surfaces extends non-linearly. Accordingly, the blockelectrodes 93, 94 constituting the respective electrode members alsoextend non-linearly in correspondence to the butt portion 96 to pressit.

In this embodiment, the butt welding of the two sheet members 91, 92executed by moving the upper block electrode 93 downward is carried outsimilarly to the embodiment of FIGS. 18 and 19.

As can be found from the embodiment, when the electrode members arecomposed of the block electrodes, the butt portion of two sheet membersmay extend non-linearly while it is impossible or difficult to butt weldthe butt portion when the electrode members are composed of theelectrode rollers. Accordingly, an effect can be obtained in that beforetwo sheet members are butted, they are manufactured by being shearedblank members in arbitrary shapes according to, for example, a shape andthe like of a product manufactured from the two sheet members asmaterials butted to each other and the butt shape of the two sheetmembers can be formed in an arbitrary shape.

INDUSTRIAL APPLICABILITY

As described above, the present invention suitably butt-welds endsurfaces of two sheet members to each other by a pair of electrodemembers applied with power and manufactures a tailored blank for forminga vehicle body of a vehicle and various kinds of members and the likeattached to the vehicle body by the butt welding.

1. A butt welding apparatus for butt welding end faces of two platemembers by electric resistance heating, comprising means for supportingthe two plate members such that the end faces abut each other and form abutt portion; a pair of electrode members disposed opposite to oneanother for performing electric resistance heat welding of the buttportion, said pair of electrode members comprising a first electrodemember provided at a first side of the butt portion and a secondelectrode member provided at a second side of the butt portion oppositeto the first side, said first electrode member being positioned so thatit extends across the butt portion and having an outer surface with apress portion and a non-press portion, the first electrode press portionhaving a stepped surface towards the butt portion, and the secondelectrode member being positioned so that it extends across the buttportion; and means for causing relative movement of the first and secondelectrode members toward each other and contacting of a surface of oneof the plate members with the first electrode member and causing the endface thereof to deform toward the end face of the other plate member,melt, and join therewith.
 2. A butt welding apparatus for butt weldingend faces of two welding sheet members by electric resistance heating,comprising: means for supporting the two welding sheet members such thatthe end faces abut each other and form a butt portion; a pair ofelectrode members disposed opposite to one another for performingelectric resistance heat welding of the butt portion, said pair ofelectrode members comprising a first electrode member provided at afirst side of the butt portion and a second electrode member provided ata second side of the butt portion opposite to the first side, said firstand second electrode members extending across the butt portion andcomprising press portions for contacting with one of the two weldingsheet members and causing the end face thereof to deform toward theother end face, melt and join with the other end face; and means forcausing relative movement of the first and second electrode memberstowards each other.
 3. The butt welding apparatus according to claim 2,wherein one of the welding sheet members is thicker than the otherwelding sheet member, said means for supporting the two welding sheetmembers comprises means for supporting the other welding sheet member ina manner such that the upper surface thereof is disposed in a planebelow a plane containing the upper surface of the thicker welding sheetmember and the lower surface thereof is disposed in a plane above aplane containing the lower surface of the thicker welding sheet memberand each of said first and second electrode members comprising a firstportion and a second portion disposed adjacent to each other, the firstportions of the electrode members being provided opposite to the thickerwelding sheet member and having a stepped surface in the direction ofthe welding sheet members as compared with the second portions of theelectrode members, which are provided opposite to the other weldingsheet member.
 4. A butt welding apparatus according to claim 3,characterized in that the first portions of the pair of electrodemembers extend toward the other sheet member across the butt portion ofthe thicker sheet member and the other sheet member.
 5. A butt weldingapparatus according to claim 2, characterized in that the two weldingsheet members have the same thickness, the means for supporting the twowelding sheet members comprise means for supporting the welding sheetmembers such that front and back surfaces thereof are aligned with eachother so as not to form a step difference, each of the pair of electrodemembers has a first portion on the side of one of the two welding sheetmembers and a second portion on the side of the other of them, the firstand second portions being disposed adjacent to each other, and thesecond portions retract in a direction away from the welding sheetmembers with respect to the respective first portions acting as pressportions.
 6. A butt welding apparatus according to claim 2, wherein onewelding sheet member is thicker than the other welding sheet member, themeans for supporting the two welding sheet members comprises means forcausing the front surface of the thicker sheet member to be aligned withthe front surface of the other sheet member or the back surface of thethicker sheet member to be aligned with the back surface of the othersheet member, without a step difference, thereby giving rise to a stepdifference between one of the front and back surfaces of the thick andthin sheet members, one of the pair of electrode members is disposed atthe surfaces of the thick and thin sheet members where the stepdifference is provided and has a first portion opposed to the thicksheet member and a second portion opposed to the other sheet member, thefirst and second portions being adjacent to one another and the secondportion projecting more than the first portion towards the otherelectrode member, and the other electrode member has a flat surface forsupporting both welding sheet members, and the portion of the otherelectrode facing the thicker sheet member and the first portion of theone electrode member act as press portions.
 7. A butt welding apparatusaccording to claim 2, wherein one of the two welding sheet members isthicker than the other welding sheet member, the means for supportingthe two welding sheet members causing the front surface of the thicksheet member to be aligned with the front surface of the other sheetmember or the back surface of the thicker sheet member to be alignedwith the back surface of the other sheet member, without a stepdifference, thereby giving rise to a step difference between one of thefront and back surfaces of the welding sheet members, one of the pair ofelectrode members is disposed at the surfaces of the welding sheetmembers aligned with each other without a step difference and has afirst portion on the side of the thicker sheet member and a secondportion on the side of the other sheet member, the first and secondportions being adjacent to one another and projecting toward the weldingsheet members in the same amount, and the other electrode member alsohas a first portion facing the thicker sheet member and a second portionfacing the other sheet member, the first and second portions of theother electrode member being adjacent to one another and the secondportion projecting more than the first portion toward the one electrodemember, the second portion of the one electrode member and the firstportion of the other electrode member are made of an electricallyconductive material, the first portion of the one electrode member andthe second portion of the other electrode member are made of anelectrically insulating material, and the first portion of the oneelectrode member and first portion of the other electrode member act aspress portions.
 8. A butt welding apparatus according to claim 2,characterized in that the pair of electrode members are composed ofelectrode rollers.
 9. A butt welding apparatus according to claim 2,characterized in that the pair of electrode members have a lengthextending along the butt portion and are composed of block electrodesfor applying a press load to the welding sheet members.
 10. A buttwelding apparatus according to claim 9, characterized in that the buttportion extends non-linearly and the pair of electrode members have ashape extending in correspondence to the butt portion.
 11. A buttwelding apparatus according to claim 8, comprising a cooling liquiddropping unit for dropping a cooling liquid onto a portion just behind aportion butt welded by the electrode rollers in the two sheet members.12. A butt welding apparatus according to claim 2, comprising anantioxidation gas supply unit for supplying an anti-oxidation gas ontoat least a portion butt welded by the pair of electrode members in thetwo welding sheet members.
 13. A butt welding method for butt weldingend faces of two welding sheet members by electric resistance heating,comprising: supporting the two welding sheet members such that the endfaces abut each other and form a butt portion; providing a butt weldingapparatus comprising a pair of electrode members disposed opposite toone another for performing electric resistance welding of the buttportion, said pair of electrode members comprising a first electrodemember provided at a first side of the butt portion and a secondelectrode member provided at a second side of the butt portion oppositeto the first side; positioning the electrode members such that theyextend across the butt portion; and pressing a surface of one of thewelding sheet members while performing electric resistance heating ofthe one welding sheet member to cause the end face thereof to deformtowards the other end face forming the butt portion, melt and jointherewith.
 14. A butt welding method according to claim 13,characterized in that one of the two welding sheet members is thickerthan the other welding sheet member, the thicker sheet member is buttedto the other sheet member such that the upper surface of the otherwelding sheet is disposed in a plane below a plane containing the uppersurface of the thicker sheet member and a plane containing the lowersurface of the other sheet member is above a plane containing the lowersurface of the thicker sheet member, power is applied to the thick sheetmember while pressing it by the pair of electrode members, and,thereafter, power is also applied to the thin sheet member by causingthe pair of electrode members to come into contact therewith.
 15. A buttwelding method according to claim 13, wherein the two welding sheetmembers have the same thickness and are butted by causing both the topand bottom surfaces of the welding sheet members to be aligned with eachother, power is applied to the one of the two welding sheet memberswhile pressing the one welding sheet member by the pair of electrodemembers, and, thereafter, power is also applied to the other weldingsheet member by causing the pair of electrode members to come intocontact with the other welding sheet member.
 16. A butt welding methodaccording to claim 13, wherein one of the two welding sheet members isthicker than the other welding sheet member, the thicker sheet member isbutted to the other sheet member by causing the top or bottom surfacesof the welding sheet members to be aligned without a step difference,power is applied to the thicker sheet member while pressing it by thepair of electrode members, and, thereafter, power is also applied to theother sheet member by causing the pair of electrode members to come intocontact therewith.
 17. A butt welding method according to claim 13,wherein one of the two welding sheet members is thicker than the otherwelding sheet member, the thicker sheet member is butted to the thinsheet member by causing one of the top and bottom surfaces of thewelding sheet members to be aligned without a step difference, and poweris applied to the welding sheet members through a path obliquely passingthrough the butt portion by the pair of electrode members while pressingthe thicker sheet member by the electrode members.